5 Lecture 4, January 15, 2024

Definition 5.1 (Combination) Given \(n\) distinct objects, a combination of size \(k\) is an unordered subset of \(k\) of the individuals. The number of combinations of size \(k\) taken from \(n\) objects is denoted \({n \choose k}\) or \({}_n C_k\) and can be computed as \[ {n \choose k}=\frac{n^{(k)}}{k!}=\frac{n!}{(n-k)!\ k!}. \]